Compression Absorption Cascaded Refrigeration System Research Articles

Multi-objective optimization of a Rectisol process integrated with compression-absorption cascade refrigeration system and ORC for waste heat recovery

The Rectisol is an essential component of coal to synthetic natural gas (SNG)/ methanol process, and its efficient utilization of energy is crucial for enhancing the energy efficiency and reducing the energy consumption in the entire coal to SNG/ methanol process. Therefore, a novel waste heat recovery system consisting of compression-absorption cascade refrigeration system (CACRS), organic Rankine cycle (ORC) and heat exchanger network (HEN) is proposed for Rectisol process to achieve the efficient utilization of energy. To realize the optimal design for the waste heat recovery system of Rectisol process, a multi-objective optimization model is established with the aim of minimizing the total annualized cost (TAC) and total exergy destroy, while simultaneously optimizing the integration configuration and operating parameters. To overcome the solving difficulties caused by large scale model and multiple optimization variables, a decomposition strategy is proposed and applied in this paper. The optimal design of a Rectisol process including 13 hot streams and 13 cold streams is conducted. Compared with the optimal schemes given in the cited literature, the total amount of waste heat recovery is increased by 19.2 %, the cooling water consumption and low-temperature cold utility requirement are reduced by 100 % and 1.7 %, respectively, demonstrating the superiority of the proposed method in efficiency improvement and energy saving. With the implementation of multi-objective optimization, the optimal scheme with both good thermodynamic and economic performances is obtained with TAC of 11,082,365 $/y and Exdestroytotal of 80,452 kW.

Thermoeconomic and environmental analyses based single objective optimization of subcooled compression-absorption cascaded refrigeration system using evolutionary techniques

ABSTRACT This article analyses a subcooled compression-absorption cascaded refrigeration system (SCRS) in comparison with a standalone compression-absorption cascaded refrigeration system (CRS) based on thermoeconomic optimization. Three different absorbent solution/solution mixture-refrigerant combinations have been tested as working pairs in vapor absorption refrigeration system (VARS), whereas four environmentally friendly refrigerants have been utilized in vapor compression refrigeration system (VCRS). The total annual cost of the system is formulated using energy, exergy, and economic performance of the system and is minimized for optimal operational parameters by implementing five recent evolutionary optimization techniques. The effect of compression subcooling on various operational parameters of the cascaded system is reported. Amid all absorbent solution/solution mixture-refrigerant-refrigerant combinations, R290 combined with (CaCl2-LiBr-LiNO3)-H2O provides the minimum total annual cost of 13,164.8 US$ yr−1 and 15,401.9 US$ yr−1 for CRS and SCRS, respectively. Sanitized Teaching Learning Based Optimization (sTLBO) and Coyote Optimization Algorithm (COA) obtain the optimal total annual cost for most VARS-VCRS absorbent solution/solution mixture-refrigerant-refrigerant combinations. Though the coefficient of performance (COP) of an optimal SCRS is about 250% higher than its optimal CRS, higher compressor work results in a higher penalty cost for the optimal SCRS, which is almost 190% higher than the optimal CRS. A quick convergence is observed for sTLBO and COA.

An efficient optimization strategy for vapor compression–absorption-based cascaded refrigeration system using various evolutionary techniques

ABSTRACT A novel optimization strategy for a compression-absorption cascaded refrigeration system (CACRS) consisting of a single effect vapor absorption system (VARS) and vapor compression system (VCRS), which employs several absorbent solution-refrigerant-refrigerant pairs to consider the combination of absorbent solution-refrigerant in VARS and refrigerants in VCRS as an optimization variable, is successfully implemented using various evolutionary optimization techniques. This article analyzes three different absorbent solution-refrigerant in the VARS with eleven different refrigerants in the VCRS. A nonlinear objective function is formulated based on exergy and environmental analysis, which is minimized using 10 different evolutionary optimization techniques. The proposed novel strategy reduces the complexity of using optimization techniques to select the best optimum absorbent-refrigerant-refrigerant pair. Differential evolution with multi-population-based ensemble of mutation strategies determined the minimum total annual cost as 13,137.78 US$/year for (CaCl2-LiBr-LiNO3-)-H2O-R152a. Lower condenser temperature and higher temperature difference in the cascade-condenser resulted in a minimum value for the total annual cost.

Multi-objective optimization of heat exchange network and thermodynamic cycles integrated system for cooling and power cogeneration

Thermodynamic cycles and heat exchange of process streams are effective waste heat recovery technologies, and their cooperation will make the use of energy more diversely and efficiently. To this end, a novel integrated system including compression-absorption cascade refrigeration system (CACRS), organic Rankine cycle (ORC) and heat exchanger network (HEN) is presented for cooling and power cogeneration and simultaneously performing the heat exchange of process streams. To achieve the optimal design of the integrated system, a thermo-economic multi-objective optimization model is developed for balancing the economic and thermodynamic objectives, along with optimizing the operating conditions and configuration structure simultaneously. Two cases in different application scenarios are studied. Compared with the literature, the economic cost and exergy destroy are reduced by 1.6% and 31.5%, respectively, demonstrating the superiority of the proposed method in improving energy efficiency and reducing energy losses. Furthermore, the conflicting relationship between economic and thermodynamic objectives is verified and the trade-off solution with both favorable economic and thermodynamic performances is determined for both cases. Compared with the optimal solutions with solo objective of economy and exergy, the exergy destroy and economic cost of the trade-off solution for case 1 are decreased by 315 kW and 50,063$/y, and for case 2 the decrease are 750 kW and 112,678 $/y, respectively.

Presenting a power and cascade cooling cycle driven using solar energy and natural gas

A configuration is presented where solar energy is parallel with fossil fuel to steadily supply a combined power and cascade cooling system. The cascade cooling system produces a steady cooling load at shallow temperatures. The variations of solar radiation during a year are considered. The system combines an improved ammonia-water power cycle with an absorption-compression cascade refrigeration system. The exhaust from the power cycle drives the absorption chiller. Working fluids are ammonia-water for absorption and power cycles and R134a for compression chiller. The effects of turbine inlet temperature, the ammonia concentration in the power cycle, boiler pressure, and generator temperature are investigated. Considering the cooling section's exergy efficiency, the generator temperature is optimized at 110.5 °C. The power cycle's boiler pressure and ammonia concentration are optimized using a genetic algorithm for various cooling loads at various turbine inlet temperature values to find the maximum annual exergy efficiency. The results show that, in all investigated cooling loads, the maximum annual exergy efficiency with a mean value of 65.66% happens at the turbine inlet temperature of 210 °C, an average boiler pressure of 58.56 bar, and an average ammonia concentration of 81.16%.

Multi-objective optimization and thermo-economic analysis of an enhanced compression-absorption cascade refrigeration system and ORC integrated system for cooling and power cogeneration

Waste heat recovery techniques can greatly improve the energy efficiency and relieve the energy crisis. The integration of compression-absorption cascade refrigeration system (CACRS) and Organic Rankine Cycle (ORC) can achieve cooling and power cogeneration utilizing waste heat. However, the simultaneous optimization of integrating configuration and operating parameters has not been considered in recent studies, neglecting the complex interactive relationship within the integrated system consequently. To overcome these limitations, an enhanced CACRS-ORC integrated system, containing more coupling possibilities and more routes in driving the integrated system with waste heat, is proposed and investigated in this paper. To examine the trade-off in the economic and thermodynamic performances, a multi-objective optimization-based method, aiming at the simultaneous minimization of the total annualized cost (TAC) and the total exergy destroy (Exdestroytotal), is developed to determine the optimal configuration and operating parameters of the integrated system. The derived Pareto solutions reveal the contradictory relationship between the two objectives, and the thermo-economic analysis is executed to show the impact of system configuration and operating parameters on economy and thermodynamics. Sensitive analysis is also performed to reveal the effects of key parameters on the structural configuration and thermo-economic performances.

Superstructure-Based Simultaneous Optimization of a Heat Exchanger Network and a Compression–Absorption Cascade Refrigeration System for Heat Recovery

Heat exchanger network (HEN) plays an important role in chemical process industry owing to its significant effect in energy recovery. Compression–absorption cascade refrigeration system (CACRS) is ...

Heat Exchanger Network Synthesis Integrated with Compression–Absorption Cascade Refrigeration System

Compression–absorption cascade refrigeration system (CACRS) is the extension of absorption refrigeration system, which can be utilized to recover excess heat of heat exchanger networks (HENs) and compensate refrigeration demand. In this work, a stage-wise superstructure is presented to integrate the generation and evaporation processes of CACRS within HEN, where the generator is driven by hot process streams, and the evaporation processes provide cooling energy to HEN. Considering that the operating condition of CACRS has significant effect on the coefficient of performance (COP) of CACRS and so do the structure of HEN, CACRS and HEN are considered as a whole system in this study, where the operating condition and performance of CACRS and the structure of HEN are optimized simultaneously. The quantitative relationship between COP and operating variables of CACRS is determined by process simulation and data fitting. To accomplish the optimal design purpose, a mixed integer non-linear programming (MINLP) model is formulated according to the proposed superstructure, with the objective of minimizing total annual cost (TAC). At last, two case studies are presented to demonstrate that desired HEN can be achieved by applying the proposed method, and the results show that the integrated HEN-CACRS system is capable to utilize energy reasonably and reduce the total annualized cost by 38.6% and 37.9% respectively since it could recover waste heat from hot process stream to produce the cooling energy required by the system.

Energy and exergy analysis of vapor compression–triple effect absorption cascade refrigeration system

In the present work, an absorption-compression cascade refrigeration system (ACCRS) has been analyzed theoretically for low temperature cooling applications. It comprises of a triple effect H2O-LiBr series flow vapor absorption refrigeration system in higher temperature section associated with vapor compression refrigeration (VCR) system using R1234yf refrigerant in lower temperature section. The cascade system provides lower temperature i.e. 223.15–263.15 K for freeze drying, pharmaceuticals, chemical and petroleum industry at lower running cost using waste available from the exhaust of gas turbine or steam turbine to run the triple effect vapor absorption refrigeration system which reduces the overall high grade energy (electricity) consumption of the cascade system. Moreover, the use of R1234yf protects the environment from global warming and ozone depletion. Energetic and exergetic analysis have been performed for the parametric investigation of the system. An EES software based computational model has been formulated for the computation of performance parameters. The analysis determines the effect of generator temperature (448.15–473.15 K), absorber temperature (298.15–313.15 K) and evaporator temperature (223.15–263.15 K) on the energetic (COP) and exergetic (exergetic-efficiency, exergy destruction rate and exergy destruction ratio performances of the system. The results illustrate that the electricity savings of triple effect cascade system are 45.84% in comparison to conventional VCR cycle. The COP and exergetic-efficiency of VCR circuit in the cascade system boost up by 85.26% and 85.28% respectively. The COP and exergetic efficiency of triple effect cascade system are higher than that of single and double effect absorption compression cascade refrigeration systems. The system circulation pump and absorber are the sites of lowest and highest irreversibility in comparison to the other system components.

Advanced Exergy Analysis of a Compression–Absorption Cascade Refrigeration System

This work presents a theoretical thermodynamic study of a compression–absorption cascade refrigeration system using R134a and a lithium bromide–water solution as working fluids. First and second law of thermodynamics analyses were carried out in order to develop an advanced exergetic analysis, by splitting the total irreversibility and that of every component. The potential for improvement of the system is quantified, in the illustrated base-case 55.4% of the irreversibility is of avoidable nature and it could be reduced. The evaporator is the component that shows a significant potential for improvement, followed by the cascade heat exchanger, the compressor, and finally, the generator. The results of the advanced exergetic analysis can be very useful for future design and experimentation of these kinds of systems.

Comparative performance study and advanced exergy analysis of novel vapor compression-absorption integrated refrigeration system

In present work, a novel configuration of vapor compression-absorption integrated refrigeration system (VCAIRS) is analyzed. Unlike previous vapor compression-absorption cascaded refrigeration system (VCACRS), proposed configuration works at lower generator temperature of 60 °C. Thus, allowing the use of low grade waste heat for its operation. The performance of VCAIRS is also compared with the equivalent vapor compression refrigeration system (VCRS) and VCACRS for the same cooling capacity of 100 kW. The comparative study result shows that electrical energy requirement in VCAIRS is 21.4% more as compared to VCACRS but it is still 63% less as compared to the equivalent VCRS. Further, the second law efficiency of VCAIRS, VCACRS and VCRS are determined to be 27.9%, 32.7% and 18.8%, respectively. Thus, both the VCAIRS and VCACRS are energy and exergy efficient configurations; but, VCACRS results in more energy efficient cooling technology in the foreseeable future as it utilizes heat at lower generator temperature as compared to VCACRS.After the comparative performance study, the exergetic performance of VCAIRS is further explored based on the coefficient of structural bonds (CSB) and advanced exergy analysis methods. Highest CSB of 4.39 is obtained for high pressure solution heat exchanger but its overall contribution in total irreversibility rate is merely 0.2%; whereas, the highest contribution of 17.4% in total irreversibility rate is by compressor 1 but CSB value computed for it is merely 1.73. Further, advance exergy analysis results show that 35.2% of total irreversibility rate of VCAIRS can be avoided by improving the efficiency parameter of components of system.

Thermodynamic and thermo-economic analysis of compression–absorption cascade refrigeration system using low-GWP HFO refrigerant powered by geothermal energy

This study proposes a simulation that incorporates energy, exergy, and economic factors into the development of an absorption-compression cycle for air-conditioning that makes use of heat sources available in Algeria. The springs have been used on record range in temperature between 60 and 94 °C. LiBr-H2O and LiCl-H2O have been used in the absorption section and low global warming potential fluids including R1234yf, R1234ze (E), and R1233zd (E) in the vapor compression section. In using these combinations of fluids, a recorded (51.36–54.16%) decrease in electricity consumption has been documented in comparison with conventional cycles. Furthermore, the coefficient of performance (COP) values for all of the combinations used ranged between (0.432 and 0.659). Enhanced performance was noted in the systems that used (LiBr-H2O/R1234yf). Economically, the use of geothermal energy is more financially sound in comparison to the use of solar energy in depth of well's less than 16 m.

Thermodynamic Modelling and Parametric Study of a Two Stage Compression-Absorption Refrigeration System for Ice Cream Hardening Plant

Abstract The present communication introduces a new concept of Two Stage Vapor Compression-Absorption Cascade Refrigeration System (TSVCACRS) for achieving low temperature industrial cooling. The system comprises of Two Stage Vapor Compression Refrigeration System (TSVCRS) having flash intercooler integrated with single stage Vapor Absorption Refrigeration System (VARS); thermally coupled by means of cascade condenser heat exchanger. The cascade condenser heat exchanger works as an evaporator for VARS and the condenser for TSVCRS. The proposed system has been designed and simulated for Havmor Ice cream Limited located at GIDC, Naroda, Ahmedabad; to check the thermodynamic performance feasibility with their existing installed TSVCRS based ice cream hardening refrigeration plant of 525 TR (1850 kW). Ammonia and LiBr-H 2 O have been considered as working fluid pair in proposed TSVCACRS. The results show that proposed TSVCACRS system would minimize the compressor work up to 28%, compared to an existing installed TSVCRS. The exergetic efficiency of the VAR, VCR subsystems and integrated TSVCACRS is found to be 32.78%, 60.29% and 53.59%, respectively. Moreover, the optimum generator temperature for the proposed system is found to be 85 °C from the energetic and exergetic point of view.

Exergoeconomic analysis and optimization of a solar driven dual-evaporator vapor compression-absorption cascade refrigeration system using water/CuO nanofluid

In this paper, a novel cascade refrigeration system integrated with flat plate solar collector is modeled and optimized. While LiBrH2O is applied as fluid pair in cascade absorption section, R134a, R1234ze, R1234yf, R407C and R22 fluids are applied in the vapor compression section and the water/copper oxide (CuO) nanofluid is applied as the heat transfer medium inside the collector subsystem. Nanoparticles volume fraction, mass flow rate of strong solution, low pressure of absorption section, collector tilt angle as well as solar collector area are selected as design parameters while the daily thermal and exergy coefficients of performance and total product cost rate are selected as three objective functions. Non-dominated Sort Genetic Algorithm-II (NSGA-II) is individually employed to achieve the final solutions of the system for the best working fluids from the thermodynamic and thermoeconomic viewpoints. The proposed system modeling represents that R134a is the best fluid from the energy and exergy viewpoints with daily energy and exergy coefficients of performance of 9.340% and 0.5815%, respectively and R1234ze with the total product cost rate of 7016 $/year is the best working fluid from the exergoeconomic viewpoint. The optimization results indicate that R134a with 2.4% and 2% improvement of the daily energy and exergy coefficients of performance, respectively, relative to the base case needs minimum collector area with amount of 680 m2 among the other working fluids. In addition, R1234ze with the total product cost rate reduction of 2.4% requires maximum nanoparticles and collector area with values of 0.041 and 702.01 m2, respectively.

Energy and exergy performance comparison of different configurations of an absorption-two-stage compression cascade refrigeration system with carbon dioxide refrigerant

This paper presents a comparative study of six configurations of an absorption–compression cascade refrigeration system. The cascade system is composed of a single-effect or a double-effect LiBr/H2O absorption chiller in cascade with a two-stage CO2 compression chiller. The cooling capacity of the absorption chiller is used to enhance the efficiency of the compression chiller. The system runs by a micro-turbine which provides the supplied energy to both chillers. System components are modeled and analyzed through the energy and exergy approaches. The performance parameters of the systems and the second law efficiency are calculated in different operating conditions. The results show that a proper choice of discharge and inter-cooling pressure along with a well calculated generator temperature can upgrade the energy utilization factor of the system considerably. It is also concluded that at a specific discharge pressure, a system with inter-cooler, after-cooler and double-effect absorption chiller would result in the highest improvement of the system.

Performance study on a low-temperature absorption–compression cascade refrigeration system driven by low-grade heat

This paper presents a performance study on a low-temperature absorption–compression cascade refrigeration system (LACRS), which consists of an absorption subsystem (AS) and a vapor compression auto-cascade subsystem (CS). In the system, low-grade heat of AS is used to subcool the CS, which can obtain cold energy at −170°C. A simulation study is carried out to investigate the effects of evaporating temperature and low-grade cooling capacity on system performance. The study results show that as low-grade cooling capacity from the AS is provided to the CS, high-grade cooling capacity increases, compressor power consumption decreases, and the COP of the CS therefore increases. Comparing with compression auto-cascade cycle, the largest COP improvement of LACRS is about 38%. The model is verified by experimental data. An additional high-grade cooling capacity is obtained experimentally at −170°C. The study results presented in this paper not only demonstrate the excellent performance of the LACRS, but also provide important guidance to further system design, and practical application.

Thermo-economic and environmental analyses based multi-objective optimization of vapor compression–absorption cascaded refrigeration system using NSGA-II technique

Present work optimizes the performance of 170kW vapor compression–absorption cascaded refrigeration system (VCACRS) based on combined thermodynamic, economic and environmental parameters using Non-dominated Sort Genetic Algorithm-II (NSGA-II) technique. Two objective functions including the total irreversibility rate (as a thermodynamic criterion) and the total product cost (as an economic criterion) of the system are considered simultaneously for multi-objective optimization of VCACRS. The capital and maintenance costs of the system components, the operational cost, and the penalty cost due to CO2 emission are included in the total product cost of the system. Three optimized systems including a single-objective thermodynamic optimized, a single-objective economic optimized and a multi-objective optimized are analyzed and compared. The results showed that the multi-objective design considers the combined thermodynamic and total product cost criteria better than the two individual single-objective thermodynamic and total product cost optimized designs.

Comparative performance study of vapour compression-absorption cascaded system at optimum condensing temperature

The present study thermodynamically analyse a vapour compression-absorption cascaded refrigeration system (CRS) that uses R407C and H2O-LiBr as refrigerants, to determine the optimal condensing temperature of cascade condenser. The optimum condensing temperature of cascade condenser is found to be 18°C for 83.09 kW refrigeration capacity at an evaporating and condensing temperature of 0.4°C and 46.8°C respectively. The optimum condensing temperature is found, to maximise the rational efficiency of CRS and minimise the total irreversibility of system. Further comparative study of CRS with equivalent vapour compression refrigeration system (VCRS) used for water chilling applications shows that the electric power consumption in CRS is reduced by 70% and COP of compression section is improved by 235% as compared to equivalent VCRS.

NLP model based thermoeconomic optimization of vapor compression–absorption cascaded refrigeration system

This paper addresses the size and cost estimation of vapor compression–absorption cascaded refrigeration system (VCACRS) for water chilling application taking R410a and water–LiBr as refrigerants in compression and absorption section respectively which can help the design engineers in manufacturing and experimenting on such kind of systems. The main limitation in the practical implementation of VCACRS is its size and cost which are optimized in the present work by implementing Direct Search Method in non-linear programming (NLP) mathematical model of VCACRS. The main objective of optimization is to minimize the total annual cost of system which comprises of costs of exergy input and capital costs in monetary units. The appropriate set of decision variables (temperature of evaporator, condenser, generator, absorber, cascade condenser, degree of overlap and effectiveness of solution heat exchanger) minimizes the total annual cost of VCACRS by 11.9% with 22.4% reduction in investment cost at the base case whereas the same is reduced by 7.5% with 11.7% reduction in investment cost with reduced rate of interest and increased life span and period of operation. Optimization results show that the more investment cost in later case is well compensated through the performance and operational cost of the system. In the present analysis, optimum cascade condensing temperature is a strong function of period of operation and capital recovery factor. The cascading of compression and absorption systems becomes attractive for lower rate of interest and increase life span and operational period.

Energy and exergy analysis of subcooling the condenser outlet refrigerant in a compression-absorption cascade refrigeration system

The main aim of the presented research is to study the effect of subcooling the condenser outlet refrigerant in a compression-absorption cascade refrigeration system via energy and exergy methods. A parametric study is also conducted to investigate the effects of the operating conditions. LiBr-H2O and H2O-NH3 are used as fluid pairs in absorption section. The system is powered up by a prime mover, which can be either a micro-gas turbine, a gas turbine or a solid oxide fuel cell. The waste heat from the prime mover operates the absorption chiller and provides additional cooling, which is used to subcool the liquid exiting the condenser of the compression chiller. Results indicate that subcooling the condenser outlet enhances the efficiency of the cycle. It is also concluded that the system with a H2O-NH3 chiller has a better overall efficiency than the system with a LiBr-H2O chiller.